Function check 

pub fn check(
    func: &Func,
    order: &Order,
    live: &Live,
    assignment: &Assignment,
) -> Vec<Problem>

Everything wrong with an allocation, in an order a person can read.

An empty answer is the one every allocation is supposed to give. Anything else is a compiler bug rather than a program the compiler cannot handle, which is why crate::run asserts on it instead of reporting it as a diagnostic.

Panics

Panics on a function with two billion virtual registers in it, which is a function no machine has the memory to hold.